The present invention relates to a multistage depressed collector for a microwave tube.
The operation of microwave tubes, such as klystrons or travelling wave tubes is based on an energy exchange between an electron beam and an electromagnetic microwave. Thus, the collector of such tubes receives, except for the energy fraction transmitted to the microwave, all the energy of the electron beam and dissipates it in the form of heat. It is necessary to attempt to reduce this dissipated energy on the one hand to reduce the difficulties associated with the removal of the heat and on the other in order to increase the efficiency of such tubes.
A known solution for reducing the energy consists of using a multistage depressed collector which comprises a plurality of electrodes arranged along the path of the electron beam of the tube. At present various geometrical configurations are used for the electrodes. Fundamentally a distinction is made between electrodes axially symmetrical with respect to the propagation axis of the electron beam from the tube and asymmetrical electrodes. These electrodes are brought to decreasing voltages and of values below those of the delay line in the case of a travelling wave tube or that of the cavities in the case of a klystron. The latter electrode can be raised to the potential of the cathode of the tube.
On reaching the collector the electron beam comprises electrons of different speeds. Under the influence of the space charge the slower electrons follow a curved path and are intercepted by the first electrode. The other electrons continue their path, their speed being progressively decreased by the retarding field existing between the electrodes and they are gradually intercepted by the collector electrodes.
Thus, the electrons are collected at the lowest possible potential, because there is a sorting of the electrons as a function of their energy.